1. Field of the Invention
The invention pertains to the art of finned tube coils.
2. Description of the Prior Art
Soldering aluminum end fittings to aluminum tubes in heat exchangers has posed a problem believed to be generally recognized. If the coils are simple one or two row coils with a simple tube circuiting arrangement and basically only return bends being used to connect the open ends of the tubes, the manufacture of such coils has been reasonably successful without an unduly high percentage of leaking coils. In our experience this has not been the case with coils having three or four or more rows and containing complex tube circuitry requiring the use of complex fittings such as tripod joints, various header configurations, and crossovers. To the best of our knowledge such coils have been made with all of the hairpin tube bights located at one end of the coil, and all of the complex fittings and return bends located at the other end of the coil. The purpose of such an arrangement of course is that all of the soldering will take place at the one end of the coil in a superheated air atmosphere (Pyronics) or by flame soldering (Selas) or in an ultrasonics process. In the Pyronics and Selas processes a reaction type flux and high temperature solder is used. The problem that we recognize in making the coil in this way is that each different type of fitting presents a different heat transfer problem in obtaining a good joint. Thus when the temperature is adequate for header joints it may be too hot for crossover joints and/or return bends and/or tripods. Thus, the joining process is simplified and made more reliable when the pieces are identical.
If the soldering of such a coil is to take place by an ultrasonic process, no opening to the interior of the coil is permitted to be immersed in the molten solder since it would create a blockage inside the coil. Such openings exist in the inlet and outlet headers which must have breather tubes attached to them to prevent the solder from getting into the tube and to provide venting during the soldering process.
When a coil is manufactured by the above methods and is found to be a leaker, it is expensive and difficult to repair the joints. In some cases where a number of the joints are sufficiently damaged, the coil is scrapped.
The aim of our invention is to provide a coil construction which, for the most part, avoids the problems experienced in the prior art.